Brightness control problem on acer aspire V5

Brightness control problem on acer aspire V5

I am running Ubuntu 12.04 LTS on new Acer Aspire V5. There is no other OS
installed. I can not control the brightness of the screen using Fn+left
and Fn+right keys. I tried to change brightness from "Brightness and Lock"
settings, bit still it does not work. Brightness control bar moves, but
brightness does not actually change.
Other people have modified the file /etc/default/grub for other Acer
models. But that solution does not work for me.
Any advise will be of much help. Thank you.